1. Field of the Invention
The present invention relates to a self-contained change speed apparatus particularly for use on a bicycle, having a drive member and a hub body rotatably supported on a fixed shaft, and a planetary gear mechanism mounted in a drive transmission path extending from the drive member to the hub body, the planetary gear mechanism including planet gears meshed with sun gears controllable to rotate on and to be locked to the fixed shaft by a control member shiftable on the fixed shaft.
2. Description of the Related Art
A self-contained change speed apparatus as noted above is known from European Patent Publication EP 0 383 350 A2, for example. This apparatus has a single planetary gear mechanism including a plurality of planet gears and a plurality of sun gears. The planet gears are supported by a gear carrier, and meshed with a ring gear. An input selector clutch selects the gear carrier or the ring gear as an input element for receiving drive from the drive member. An output selector clutch selects the gear carrier or the ring gear as an output element for supplying the drive to the hub body.
The sun gears are controllable by the control member through externally operable one-way clutches disposed between the sun gears and fixed shaft. Controls of the sun gears are complicated since, depending on the input element selected by the input selector clutch, forces are applied in different directions for stopping rotation of the sun gears. As a result, the control member and adjacent components have complicated constructions. Specifically, as shown in FIG. 24a, when a force F1 is inputted to the gear carrier supporting planet gears 120b, with the ring gear 150 acting as an output element subjected to a load F2, a reaction F3 is produced against a moment M1 resulting from F1 and F2. Therefore, clockwise rotation (in FIG. 24a) of the sun gear 120a must be stopped. On the other hand, as shown in FIG. 24b, when the force F1 is inputted to the ring gear 160, with the gear carrier acting as the output element subjected to the load F2, a reaction F3 is produced against a moment M3 resulting from F1 and F2. In this case, counterclockwise rotation (in FIG. 24b) of the sun gear 120a must be stopped. Thus, a construction is needed to stop opposite rotations of the sun gear relative to the fixed shaft. For this purpose, the above prior apparatus includes two one-way clutches having different directions of transmission, and means for breaking one-way drive transmission, more precisely variable speed drive transmission through the planetary gear mechanism with the sun gears maintained stationary. This results in a complicated construction. This problem is particularly serious where a multi-planetary gear mechanism is employed in which a plurality of planetary gear mechanism are interconnected in order to provide multiple speed stages. Where a plurality of such planetary gear mechanisms are simply interconnected, a plurality of output selector clutches are required for selecting the output element for supplying drive to the hub body. Controls of these clutches are complicated and require a large overall construction of the apparatus.